The present invention relates to a method and apparatus for submersion and installation of primarily heavy fundament structure on the sea bottom in connection with relatively large depths.
Submersion and accurate positioning of large fundament structures at relatively large depths, for instance more than 350 meters, are difficult to accomplish on the basis of known techniques. Large crane vessels of the type utilized for offshore operations are not designed for submerged lowering of large heavy structures to large depths, and such crane vessels have at present a limit of a depth of approx. 350 meters, and approx. 350 and 5000 tons lifted weight. If the depth exceeds 1000 meters, the weight of the hoisting cable will be so large that the effective installation weight will be rather limited. At very large depths, the entire loading capacity of the cable will be utilized in order to carry its own weight.
Several known methods and apparatus for submersion and installation of heavy structures on the sea bottom have been developed by the applicants, and are, among others, shown in U.S. Pat. No. 4,909,671 and pending application Ser. No. 745,238.